Abdominal aortic aneurysms (AAA) are a leading cause of death among the elderly. The majority of AAAs are clinically silent and the mortality rate associated with rupture is about 90%. Abdominal ultrasound is a safe and reliable method to detect AAAs and identification of high risk individuals is crucial to a cost-effective screening program. A study is underway to determine the genetic etiologic determinants of AAA. We will determine the extent to which siblings of AAA patients are affected. Preliminary data indicate that siblings of female patients are more susceptible than siblings of male patients. We will explore this hypothesis and, if indicated, preferentially collect affected sibships through female probands to provide a genetically enriched sample for future linkage studies.